Industrial-rated circuit breakers such as those described in U.S. Pat. No. 4,754,247, which Patent is incorporated herein for reference purposes, are often times mounted within an electrical enclosure that is remote from the protected electrical equipment. When the electrical equipment is shut down for maintenance and repair, the associated circuit breaker is turned to its OFF condition and some type of interlock means is generally employed to prevent the circuit breaker from being inadvertently turned to its ON condition.
U.S. Pat. No. 3,595,040 describes a handle lock attachment whereby a padlock is employed to ensure that the circuit breaker operating handle remains in a fixed position.
U.S. Pat. No. 2,169,860 describes the use of a circuit breaker guard member and locking bar to prevent access to the circuit breaker handle or to the attachment means for holding the padlock support to the circuit breaker cover.
U.S. Pat. No. 4,882,456 utilizes a pair of upstanding flanges one on either side of a circuit breaker operating handle having a pair of apertures aligned with an aperture in the circuit breaker handle for preventing movement of the handle.
In those rare instances where the short circuit current through the protected circuit exceeds the rating of the associated circuit breaker, the circuit breaker contacts can become welded in their closed position by the intense heat generated at the interface between the opposing contact surfaces. The so-called "welded contact" condition prevents the circuit breaker operating handle from remaining in its "OFF" position by the return bias provided by the circuit breaker operating mechanism springs. Although the handle can be manually moved to its "OFF" position, the handle readily returns to its "ON" position upon release thereof. Should the operating handle be moved to its "OFF" position and secured by means of a padlock such as described in the aforementioned U.S. Patents, the "OFF" position of the operating handle mistakenly infers that the circuit breaker contacts are separated when they are, in fact, welded together in their closed condition.
One purpose of this invention is to provide a circuit breaker handle interlock arrangement whereby the circuit breaker handle can only be locked in its OFF position when the circuit breaker contacts are actually separated.